The present invention relates to an intracranial pressure relief valve and, more particularly, to a single-piece combination valve stem and fluid flow restrictor for use in a three stage valve of the type which provides either constant pressure or constant flow characteristics in accordance with a fluid pressure differential applied across the valve.
Hydrocephalus is a condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) collected in the ventricles of the brain. The excessive collection of the CSF in the ventricles results in an abnormal increase in both epidural and intradural pressures. This may in turn cause a number of adverse physiological effects including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism.
Treatment of the hydrocephalic condition frequently involves relieving the abnormally high intracranial pressure. To this end, a variety of CSF pressure regulator valves and methods of controlling CSF pressure have been developed which include various check valves, servo valves or combinations thereof. Generally, such valves serve to divert CSF from the ventricles of the brain through a discharge line to some suitable drainage location in the body, such as the venous system or the peritoneal cavity. The check valves operate by opening when the difference between CSF pressure and pressure in the discharge line exceeds a predetermined level.
The use of a simple check valve in the treatment of hydrocephalus is potentially disadvantageous since it is possible for such a valve to open in response to a sudden, but nevertheless perfectly normal, increase in differential pressure between CSF in the ventricular spaces and fluid at the selected discharge location of the body, resulting in abnormal and potentially dangerous hyperdrainage of the ventricular spaces. For example, when a patient stands after lying in a recumbent position, the resulting increased vertical height of the fluid column existing between the head and the selected drainage location may result in such an increase in differential pressure. Accordingly, the valve described in the copending application of the present inventor, Ser. No. 672,868, abandoned in favor of Ser. No. 930,048, filed Nov. 12, 1986, has been developed which serves to prevent undesired hyperdrainage by limiting the flow rate of fluid through the valve when a sudden increase in differential pressure occurs.
In this valve, a diaphragm, movable in response to the pressure differential between ventricular CSF pressure and pressure of fluids at the drainage location of the body, included a valve seat movable with the diaphragm, such valve seat having a fluid metering orifice extending therethrough. The inner surface of the valve seat was provided with a precisely defined valving surface which in cooperation with a valve closing sphere or check valve, as well as a fluid flow restrictor, provided a three stage effect. By controlling the position of the sphere the valve seat and the restrictor as well as the configurations thereof, it was possible to establish four conditions of valve operation including three stages of controlled fluids flow. The first condition, not constituting a stage of fluid flow, included operation of the check valve against the valve seat to prevent fluid flow through the orifice. The second condition of operation, constituting the first stage of fluid flow, included movement of the diaphragm and valve seat away from the check valve or sphere in response to a first predetermined fluid pressure differential to permit limited flow of fluid through the orifice. The third condition, or second stage of fluid flow, occurred in response to sudden changes in fluid pressure differential such, as that resulting from a rather extreme change in physical position of the patient, with the result that the diaphragm moved further relative to the check valve and the restrictor entered the fluid flow orifice to become cooperatively effective with the valve seat to control fluid flow at a substantially constant rate thereby avoiding hyperdrainage. The fourth condition, or third stage of fluid flow, resulted from further movement of the diaphragm and valve seat relative to the restrictor to control further fluid under under conditions of a predetermined second substantially constant pressure differential.
A CSF pressure relief valve is typically miniaturized for implantation and is required to perform with a high degree of precision under highly demanding conditions throughout a rather extensive, ever-changing mode of operation. Consequently, it has been necessary to carefully control the dimensions of the various parts of the valve, particularly the valve seat, the valve stem assembly and the orifice defined by the valve seat. The parts involved are quite small, and working tolerances on the order of 0.0001 of an inch must be met. Considerable manufacturing costs may be incurred in constructing such a valve.
A CSF pressure relief valve incorporating a one piece valve stem is described in the copending application of the present inventor, Ser. No. 608,137, filed May 8, 1984, now U.S. Pat. No. 4,627,832, issued Dec. 9, 1986. The present invention is directed to an improvement in such a valve wherein the number of manufacturing steps, and hence the cost of the valve, is reduced. Basically, a valve constructed in accordance with the present invention is provided with a comparatively simply constructed valve seat, the inner surface of the seat which defines the fluid flow orifice not being primarily relied upon to establish the various conditions or stages of fluid flow, such conditions or stages being primarily dictated by a specially configured one-piece valve stem received in the orifice. The desirable flow characteristics are primarily governed by the shape of the valve stem or pin, with the valve seat merely defining the orifice and, in conjunction with the shape of the stem establishing the flow restriction characteristics as described.
In view of the foregoing, it is a general object of the present invention to provide a new and improved pressure regulator valve for relieving intracranial pressure caused by the presence of excess CSF in the ventricles of the brain.
It is a more specific object of the present invention to provide a pressure regulator valve which includes components which may be easily and economically manufactured.
It is a still more specific object of the present invention to provide a pressure regulator valve in which critically dimensioned components are of an easily manufactured configuration.